The oxides of nitrogen, especially nitric oxide and nitrogen dioxide, are noxious gases which are common combustion products found in stack gases from furnaces fired with coal or other fuels. Because the oxides of nitrogen, hereafter referred to as NO.sub.x, are primary contributors to the creation of photochemical smog and its accompanying health problems, the amount of these gases which may be released into the atmosphere is limited. Nitrogen dioxide is readily soluble in certain scrubbing solutions such as sodium hydroxide and sodium hypochlorite, but nitric oxide is not very soluble in most aqueous solutions. Therefore, it is usually necessary to oxidize the nitric oxide present in a stack gas to nitrogen dioxide before the gas stream may be scrubbed to effectively remove the NO.sub.x.
Chlorine dioxide has been taught as a means for oxidizing nitric oxide to the more soluble nitrogen dioxide prior to scrubbing (U.S. Pat. No. 4,035,470), but in general the oxidation of nitric oxide using chlorine is too slow to be of practical value in commercial operations.